Skin peeling protects against sun-linked cancers

WASHINGTON (AP) - Sunburns may be painful, but new medical research shows that the skin peeling following a burn is one way the body protects against skin cancer.

In mouse studies at the University of Texas M.D. Anderson Cancer Center, researchers found that sunburned skin makes a protein that kills any cells with mutations that might otherwise lead to cancer. The damaged cells are then sloughed off.

"Our finding is the first to identify a protein that is a natural defense against skin cancer," said Laurie Owen-Schaub, senior author of a study published today in the journal Science.

Skin cancer is the most common form of cancer. About 1 million cases of basal cell and squamous cell cancer are diagnosed annually in the United States. The most serious form of skin cancer, melanoma, is diagnosed in about 44,200 Americans annually. Skin cancer can be easily treated if detected early, but the disease kills about 9,200 Americans annually.

Exposure to ultraviolet radiation from the sun is thought to be the most common cause of the genetic changes linked to skin cancer. Studies have shown that UV radiation can disable certain genes that normally keep cancer in check.

Owen-Schaub said her team found that a protein called "fas" is the key to protection against sun-linked skin cancer. Fas helps to eliminate those cells that are a cancer threat because they have been genetically damaged by the sun. In effect, fas directs a suicide process that causes mutated cells to kill themselves.

"It is a mechanism that we have evolved biologically to deal with the everyday exposure to UV that we get," said Owen-Schaub.

If a cell has only a small amount of damage to its DNA, then it will just repair the damage and continue to function normally. But when there is a great deal of damage, such as happens with a sunburn, there is only one solution.

"With an excessive amount of DNA damage, the cell will just eliminate itself because the repair could miss some of the mutations that could be critical in skin cancer," she said. It is the death of these gene-damaged cells that causes the skin to eventually peel away after a sunburn, but basal cells just beneath the outer skin can also be genetically damaged by the sun and eliminated by the fas process.

In their study, the University of Texas researchers used two types of mice. One mouse strain had the normal ability fas process. The other mouse type did not.

When both groups of mice were exposed to UV radiation for two weeks, the researchers found, only one in 20 of the mice with the fas protein had skin cells that had been genetically altered by the simulated sunlight. This showed that the fas suicide process had detected genetically flawed cells and caused those cells to die, Owen-Schaub said.

Among the mice without the fas process, however, or 14 out of 20, or 70 percent, had skin cells with UV-damaged genes. Such genetic damage is a precursor to skin cancer.

Although the study was only in mice, earlier studies have shown that many of the cellular actions of fas are the same in both humans and mice. Owen-Schaub said her team next will be checking for the level of fas activity in human patients who already have developed skin cancer.